


Sin

by Safiyabat



Category: Supernatural
Genre: Dark Dean Winchester, M/M, Mark of Cain, Smart Sam, Unrequited Castiel/Sam Winchester
Language: English
Status: Completed
Published: 2014-04-23
Updated: 2014-04-23
Packaged: 2018-01-20 12:03:43
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,714
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1509785
Author URL: https://archiveofourown.org/users/Safiyabat/pseuds/Safiyabat
Summary: <blockquote class="userstuff">
              <p>Castiel is with Dean, but Dean is not the Winchester he's thinking of.  Unfortunately this is not the time for making a change.</p>
            </blockquote>





	Sin

**Author's Note:**

> This was written for the anonymous prompt at spnkink-meme on LJ:
> 
> Cas is with Dean but he actually loves Sam and for whatever reason they can't be/aren't together (possible reasons could be: unrequited Sam/Cas, Cas is being coerced to being with Dean, Cas is just too shy to say anything & Dean initiated it etc).  
> Basically I want Cas with Dean but thinking of Sam the whole time.
> 
> Just as a warning, this fic deals with the effects of the Mark of Cain and as such is not necessarily Dean-friendly.
> 
> Supernatural and the characters from the show are not my property. I make no money from this or any other work of fan fiction.

Cas heard the footsteps echoing down the hall and he couldn’t help but feel a stirring deep in the center of his being. He didn’t need to see the body associated with those footsteps to know that they belonged to the younger Winchester brother. He could sense that shining soul even through the bunker’s warded walls, too bright for even an angel to view directly for long. The thought made the hair on his vessel’s arms stand up. “Your brother is home,” he informed Dean. 

The elder Winchester grunted, taking a drink from his glass. “Did he leave?” His vessel’s eyes couldn’t pick up the Mark’s effects on him but his angelic senses couldn’t avoid them, muting some tones and brightening others. Those notes – brassy, jarring, sharp and out-of-tune with the body and soul Castiel had put back together all those years ago – muted when Cas touched him. It didn’t mean that the other notes brightened or intensified but at least the horror of the bloodlust and rage decreased. 

“Yes,” Cas replied. “He said he had a case.”

“We already have a case. Abaddon.” There it was, a spike of a de-tuned oboe or maybe a zurna. “Or is that just not his problem anymore?” 

“He didn’t tell me what case he was working on. He mentioned someone named Carlos.” Cas wasn’t proud of the spike of jealousy that ran through him then.

“I don’t know any ‘Carlos.’” Dean frowned. “Think this is something like Ruby? Have you met this guy? Have you seen him?” 

The footsteps stopped and Sam was there. “Hey,” Sam greeted, a motorcycle helmet under his arm. The beautiful hazel eyes in which Castiel could happily lose himself for days were ringed with purple and his hair hung limp from having been under the helmet. He looked tired and he definitely favored his right side. “Ruby’s been dead for years, Dean. I learned from my mistake.”

“Did you?” Cas put a hand on Dean’s arm and felt his lover’s muscles relax, sensed those angry discordant tones returning to a less toxic state. 

“Anyway. Carlos caught wind of another little factory outside of Santa Fe. We took care of it; nothing to worry about.” 

Cas’ head tilted to the side, involuntarily. “You’re hurt.”

“It’s nothing to worry about, Cas,” Sam waved with a gentle little half-smile. “A couple of the soulless people got a little frisky, that’s all. You know how people get when they don’t have their souls. And the demons really didn’t want to go gently, you know? But no big deal, I’m okay. Carlos patched me up and I’ll be right as rain in a day or two.” He shifted, breathing shallow. “Anything new on your end?”

“Whole steaming pile of nothing. It would have been more useful if you’d had been here,” Dean pointed out, “researching, instead of capering around New Mexico.” 

Cas blinked. “Dean, Sam was keeping souls from joining Abaddon’s demon army. That’s important work.” He glanced at Sam but the giant had already staggered back toward his room.

He turned back to Dean, who slumped again. “I just can’t… I just can’t stop myself,” the human muttered. “I just get so…” 

Cas put his arms on Dean’s shoulders and rubbed carefully, noting the knots that hadn’t been there only an hour before. “It’s the Mark,” he assured his lover. Well, it was mostly the Mark. Not entirely, but mostly. “It exacerbates things. It did for Cain.” Too late of course he realized that reminding Dean of the fate of his demonic mentor’s younger brother might not have exactly been polite.

“I’m scared, Cas. I don’t know if I’m going to be able to control myself.”

Perhaps you shouldn’t have taken a mark created by Lucifer without learning more about it, Cas thought viciously. He didn’t say anything, though. Instead he rubbed Dean’s freckled shoulders, and if he was thinking of broader, more bronzed shoulders that he might have preferred beneath his hands then what of it? Dean accepted his touch, and he gave it freely. He should learn to be content with it.

***

“Cas? Can I borrow you for a moment?” 

Heat exploded in the angel and traveled through all of his limbs. Sam’s slightly raspy, diffident voice brought him out of the tome he’d been perusing, a dusty old volume of demonology that he shouldn’t have even needed to glance at. How Sam had even managed to sneak up on him like that was a mystery. A human male of his size should not be able to move so silently. It wasn’t natural. “Of course, Sam,” he made himself say even though his mouth went dry when he saw the Winchester. A small furrow had appeared on his brow as it often did when something troubled him. In later years, on the off chance that his lifestyle did not kill him before he reached his later years, it would form a full-fledged and endearing wrinkle. “How may I be of assistance?”

“I wanted to run something by you in the lab.” He glanced at Dean briefly. Dean just snorted and looked back at his pile of research, the pile that hadn’t changed in three days. 

Cas followed Sam down the hallways and to the lab. The man still limped although it wasn’t as pronounced as it had been. “I wish you’d let me heal you, Sam,” he blurted out.

“I’ll be fine, Cas,” Sam replied gently. His voice was always gentle, had even been gentle when Cas had broken the Wall holding his sanity together after Hell. Angels were supposed to incarnate God’s love and forgiveness but Cas knew better. He knew that Sam Winchester was the living manifestation of God’s Grace. “I wanted to talk to you about something.” 

The Men of Letters had housed the lab in a part of the bunker that was as far from the library and the garage and the gun range as it could possibly be, as though someone had been afraid that something might ignite and cause a reaction. He supposed that was a not-unreasonable assumption given the kinds of material the Men of Letters worked on. Chemical reactions were bad enough but when magic was added to the mix all sorts of things could go terribly awry. He sometimes suspected that Sam blew things up in there just for fun, when the occasional cloud of sulfur or ammonia or sometimes even ozone reached him. It was healthy for humans to have hobbies, he supposed.

Within the lab Sam had a number of notes spread out on the black-topped table and some kind of elaborate obsidian amulet suspended over a tripod over a Bunsen burner. The vague smell of scorched angelica root overwhelmed his nose, although there were a few undertones he couldn’t quite detect. “What is that?”

“That,” Sam sighed, “is an amulet. I’ve been working on it for a while. Carlos has been helping me.”

Carlos again. Cas sighed. “Who is Carlos, Sam?”

“Carlos? He’s a scientist – a chemist, actually, from down near Santa Fe. He’s a brilliant guy, made it through his Ph. D. program in like two years which is unheard of.” His hazel eyes got a kind of faraway look for half a second. “He’s also a brujo.” 

Cas blinked. “Isn’t that incompatible with hard science?” 

“Not really. It’s just a different set of parameters.” He shrugged. “He comes from a long line of practitioners, actually. So yeah. Anyhow. I mentioned the issue with the Mark and how it was having some exciting side effects –“

“You told someone about Dean bearing the Mark of Cain?” Cas turned on him. 

“I put it in terms of a curse,” Sam assured him. “I didn’t tell him specifically about Cain, although he saw some of what I was researching. Anyway, he helped me with some of the research based on what he knows, what his family knows, what he learned from his own contacts. He’s got a lot of knowledge that the Men of Letters would have dismissed out of hand back in the day, you know? Native lore, Mexican lore – anyway. He had some suggestions, and I came up with some stuff too, and then we managed to find some stuff that we thought might help. It was a really good collaboration – or it will have been, if it works.” 

“Nothing can remove the Mark, Sam,” Cas informed him gently. He reached out to put a hand on Sam’s arm. It was purely to reassure him, of course. No other reason. Not to feel the hard muscle beneath the tanned skin, or the warmth of that bright soul contained within the magnificent body. “Even sharing the Mark with Dean didn’t remove it from Cain, from what Dean told me.”

“No, I know, Cas.” He glanced down at Cas’ hand and that’s when Cas noticed the bruise.

“Is that from Carlos?” Rage welled up in the angel, or perhaps wrath would have been a better word.

“What? No! I told you, there were a bunch of soulless people to fight and then a bunch of demons. No big deal. I’m a little banged up.” He shrugged, removing the hand before Cas could actually heal him. “Look. We thought that this amulet might help to… draw off some of the negative energies around Dean. Some of the side effects from the Mark,” he continued as Cas stared. “I know you’ve been helping – and I totally get how much you’ve been helping, believe me. But it’s been getting worse.” 

“I was hoping you wouldn’t notice,” Cas whispered. 

“Kind of hard not to,” he huffed with that gentle smile of his. “He’s always been kind of… aggressive… in certain ways but this is exceptional. Like I said, I know you’re helping. You’re doing a lot to help, you’re keeping him on such a more even keel than anyone could have expected. I know I have you to thank. Anyway, I’m hoping that this will help him to control himself before he gets to a point where he can’t actually do that anymore, you know?” 

The angel regarded the trinket. “It has power,” he admitted, feeling the energy contained in the stone. “Carlos gave it to you?”

“We came up with the spells and everything together,” he admitted with a smile. “A little bit from Babylon, a little bit from Teotihuacan, a little bit from Santa Fe, a little bit from Rome.” He shrugged. “If it works, right? Anyway, I was kind of hoping that you could give it to him.”

Cas pulled back. “Me? Why?” He didn’t want to take credit for Sam’s idea; Sam had little enough credit for the things he’d accomplished already. He deserved to be acknowledged for the things he’d done.

“The Mark has a very specific effect. He’s aggressive in general but exceptionally angry at me and anything to do with me. He wouldn’t take it; he wouldn’t trust it if he knew I’d had anything to do with it at all. It needs to come from you.” Those eyes of Sam’s turned to him and pleaded with him again, independent entities with their own will. “You know it’s true.” 

He sighed. It wasn’t like he could pretend Sam was wrong, or fight the power of those eyes. “Yes. I’ll give it to him tonight.” 

Sam smiled – the first time the angel had seen a true smile on the man in years, with the dimples and everything. “Awesome, Cas. Thanks.”

“Don’t mention it.”

***

Dean and Castiel retreated to Dean’s room after dinner. Cas wasn’t entirely sure if it was a retreat for private romantic time or simply to be away from Sam. If it was the latter it was completely unnecessary; Sam rarely interacted with them these days as seemed to be a preference for both brothers. If it was the former Cas might have been forgiven for his uncertainty. Dean sat on the bed, face stony and breathing tense. Cas approached. “I have a gift for you,” he said after a moment.

Dean startled a little. Cas could sense the off notes in his soul, the taint rising in him. The bloodlust of the Mark had been stirring in him again. “For me, Cas?” Dean’s grin was wicked. “You shouldn’t have.”

“On the contrary.” He made himself smile and straddle Dean’s lap, earning a crooked grin from the hunter. The hunter who was his actual partner, he reminded himself. The one to whom he’d committed himself long before the Apocalypse. “I think you’ll find this helpful with some of the side effects you’ve been experiencing.” 

One sandy eyebrow ascended slowly. “Care to elaborate?”

“It won’t take the Mark away.”

“I wouldn’t want it to,” Dean reminded him. “The whole goal is to ice Abaddon, remember?”

Why the rulership of Hell was of any interest to someone who had once been assured a place in Heaven was beyond Castiel but he refrained from comment. “Of course. But you did express some concern about being in control of it and this should help with that.” He pressed the amulet into Dean’s right hand. He’d thought about putting it on Dean himself, but he didn’t think that would exactly sit right with Dean’s mindset right now. Dean needed to be in control, he needed to feel himself to be in control. “Will you put it on?” 

He made a face. “What is it, Aztec or something?” 

Carlos, Cas thought spitefully. “Or something,” he told him, kissing Dean’s full lips. “It should be useful, should it not?”

Dean slipped the leather thong over his neck. “I guess we’ll see. You’d know if it was a load of crap, right?”

“I would not mislead you on such a thing, Dean.”

Dean kissed him then, rough and demanding. Cas responded, because that was how sex with Dean had become since he’d taken the Mark. Not, he reflected, that he had much to compare it to. It was okay though. He loved Dean, he’d always loved Dean and he would always love Dean. He’d committed himself to Dean before he’d even raised him from the Pit. It had been God’s plan that he should love Dean.

Had it been God’s plan that he love Dean in this way though? He enjoyed sex, and he’d enjoyed sex with Dean, but he couldn’t help but wonder if the sex might not be different with the younger Winchester. If he might not be more receptive to the nuances of intercourse with a being of grace and light. If he might not be more sensitive to the subtle cues Cas tended to give. If Cas himself might not need to be so very careful about holding himself back at the moment of climax. 

When Dean finished Cas zapped them both clean. He held his lover until he fell into a deep, dreamless sleep and then he dressed himself and left to pursue more research. When he passed Sam’s room he heard the younger Winchester on the phone. “No more soulless problems by you, Carlos?” Sam sounded tired, but he could hear the smile in his friend’s voice. There was a pause. “Okay. Good. Glad to hear it. No, no. I gave it to his partner to give to him. There’s no way he was going to take it from me, you know?” The bitterness in his voice on that one sentence cut even through the door but disappeared when he spoke again, soft and sweet. “Yeah, I know. Hopefully it will help. And thank you for all your help, man. I couldn’t have done much without you.” 

Cas stormed off to the library, trying to restrain his cursing of the mysterious Carlos to his language. He didn’t want an angel’s jealousy to be responsible for taking someone away from Sam if that someone made him happy. 

***

The amulet had some effect. It wasn’t a cure-all of course but Cas hadn’t expected it to be. The Mark couldn’t be removed, only temporarily softened. The morning after the amulet was given Dean woke up refreshed and even gave Cas a small but genuine smile and a kiss. He still avoided Sam in the common areas but when Sam came into the library he restricted himself to tensing up and didn’t lash out with his words. Castiel, who was watching his soul, could see the brassiness and the sharpness swell slightly but they seethed down again immediately, dropping back to a dull roar. 

Sam kept his face from showing any pleasure or pride in the accomplishment of course. Even the slightest hint of his involvement would undo everything. Instead he collected the tomes he felt he needed and retreated to his monk’s cell. Cas tried to focus on the books he himself had chosen, but couldn’t help but get distracted by the image of a tall, chestnut-haired man with hazel eyes. 

The next day Sam actually ventured into their company to give a report. “So it looks like there’ve been some heavy signs of demon activity around Laredo, Texas,” he informed them. “We’ve got the usual crop failures, bad weather, insect infestations –“

“Right. Lots of demon signs. Your point?” Dean’s words were harsh and Cas could sense the anger and bloodlust in him, but he managed to keep it under control. The hunter’s tone was light as he grabbed his boyfriend’s hand. 

Sam cleared his throat. “Yeah. Right. My point is that I suspect that Abaddon may be stepping up activity there and I think it might behoove us to check it out.”

The blond snorted. “’Behoove us.’ Who talks like that?”

“I do. Look, I’m happy to go alone, really I am, but assuming she is there do you really want to miss an opportunity to grab her?”

Dean sighed. “Fine,” he growled. “I’ll call Crowley.” He got up and left the room. 

Cas turned to Sam. “Would this have anything to do with Carlos being in New Mexico?” 

Sam blinked. “I wouldn’t want Carlos anywhere near Abaddon, Cas,” he told the angel. “I mean, I don’t even like him fighting demons, you know? I know he’s competent but…” 

“But you worry about him.” Cas made himself smile a little, and if the smile was a little sad he could only hope that Sam wouldn’t pick up on the reasons for it. 

“Well yeah. I mean, he’s smart, he’s crafty, he’s really good at what he does – he’s too valuable to risk on dumb crap, you know?” He let his mouth curl up a little. 

“I’m sure you’ll be very happy together. You seem to care for him very much.” 

If Sam had had a drink he’d have choked on it. “Cas, it’s – it’s not like that. Me and Carlos? No. It would never happen, okay?”

“Why not? You care for him, he seems to be eager to work with you.” He walked forward, placed a hand on Sam’s shoulder. 

“Because he knows the truth about me, okay? Carlos knows who I am. He knows what I am,” he continued, looking away. “No one who knows me – who actually knows me – would ever want anything to do with me. He’s a good man. He should be allowed to stay a good man, all right?” 

“Sam,” Cas began. He’d have said more, not that he knew what to say, but Dean interrupted by returning to the room. “Something I should know about?” he demanded mildly, raising his eyebrows.

“No one’s keeping anything from you, Dean,” Sam sighed. “I’m going to get my stuff.” He left the room, disappearing as quickly and as silently as if he’d teleported. 

Dean’s green eyes stared at Cas for a moment. “You know,” he said after a second, “I’m not an idiot.” 

Cas frowned. “I have never suggested that you were.”

“I’ve seen you watching him. Ever since you got back from Purgatory I’ve seen you watching him.”

“He is pleasing to the eye,” the shorter man shrugged. “It hasn’t gone unremarked-upon.” 

“He wouldn’t, you know.” 

“Wouldn’t what?” 

“With you. Even if you left me. You’re an angel.” 

“I’m not leaving you, Dean. But Sam used to revere angels.”

Dean snorted. “Yeah, sure. That was before.”

“Before the Cage.” Cas shivered. He could still remember his own Harrowing of his brothers’ cell and the things he’d seen being done to the man in there. 

“Before meeting angels. Before you and Uriel rejected him. ‘The boy with the demon blood,’ you called him.” Dean grinned and there wasn’t anything nice about that grin at all. “See Sammy, when he gets all feverish or hallucinating, he gets kind of chatty. And of course you’re the first one to actually call him an abomination.” 

Cas sighed. “It is true. It was a technical term; I did not intend to be hurtful. I know now of course that I was.” He shrugged again. “But Dean – that’s not important. I know that he doesn’t want me, and I don’t care. I’m not leaving you.” He couldn’t. He’d committed to Dean too thoroughly to back out, and besides Cas’ presence was largely responsible for keeping Dean’s changed personality in check where is brother was concerned. He had to stay with Dean to keep Sam safe.

Besides, he loved Dean. He did. And Dean was probably right. Angels had done horrible things to Sam. Cas himself hadn’t always treated the man well, a fact that would gnaw at his heart for all of eternity. Sam’s capacity for forgiveness was the stuff of legend or would be if anyone were paying attention or cared about that sort of thing, but even he could not possibly be expected to extend himself thus far. He wished he’d had the chance to respond to his beloved’s self-deprecating words, though. He knew Sam – he knew who and what Sam was, he knew the truth, and he loved Sam more than some stupid scientist who happened to know a little bit about demons and witchcraft. If Carlos couldn’t love Sam for all of that then he wasn’t half as brilliant as Sam made him out to be. “I’m not leaving you, Dean,” he said again, taking the hunter’s hand. 

Dean’s smile now was smaller, more genuine. “I know you won’t, Cas.” He placed a kiss on his lips. “I know you won’t.”


End file.
